Image monitoring and control system

ABSTRACT

An automatic replenishment system for a film processor comprises an optical sensor and associated circuit for monitoring and integrating the optical densities developed in sheets of image bearing photosensitive material, to control the feeding of replenishment chemicals to the film processor. An improved sensor is employed wherein scanning occurs at constant speed to permit use of an integrator having a fixed integration time; and the integrator is activated as a function of the distance that an image-bearing photosensitive sheet has been transported past the sensor. A rebalancing zeroing circuit automatically adjusting the monitoring system for each scan is added to improve overall accuracy without requiring regulated power supplies.

KR arssmloa uuucu QtaLCS IdlClll [72] Inventors John N. StreetAlexandria; William 1. Brady; Walter L. Mclntosh, Woodbridge, Va. [211Appl. No. 858,719 [22] Filed Sept. 17, 1969 [45] Patented Jan.12,1971[73] Assignee Logetronics lnc. Springfield, Va. a corporation ofDelaware Continuation-impart of application Ser. No. 734,297, June 4,1968.

[54] IMAGE MONITORING AND CONTROL SYSTEM 9 Claims, 3 Drawing Figs.

[52] US. Cl 95/89, 95/94; 350/96 [51] Int. Cl G03d 3/06 [50] Field ofSearch 95/89, 94; 350/96 [56] References Cited UNITED STATES PATENTS1,895,760 1/1933 Hunt 95/89 2,296,048 9/1942 Planskoy 95/89 2,631,5113/1953 Tuttle 95/89 3,388,652 6/1968 Parrent, Jr. 95/89 3,453,944 7/1969Craig 95/94 3,472,143 10/1969 Hixon et a1. 95/89 FOREIGN PATENTS1,105,476 3/1968 Great Britain 95/89 Primary Examiner.lohn M. l-loranAssistant Examiner-Robert P. Greiner AttorneysWilliam D. Hall, ElliottI. Pollock, Fred C. Philpitt, George Vande Sande, Charles F. Steiningerand Robert R. Priddy ABSTRACT: An automatic replenishment system for afilm processor comprises an optical sensor and associated circuit formonitoring and integrating the optical densities developed in sheets ofimage bearing photosensitive material, to control the feeding ofreplenishment chemicals to the film processor.

An improved sensor is employed wherein scanning occurs at constant speedto permit use of an integrator having a fixed integration time; and theintegrator is activated as a function of the distance that animage-bearing photosensitive sheet has been transported past the sensor.A rebalancing zeroing circuit automatically adjusting the monitoringsystem for each scan is added to improve overall accuracy withoutrequiring regulated power supplies.

Control Circuit.

PATENTEU JAN 1 2 IQII SHEET 2 [1F 2 From Transport Pulse GeneratorMechorticol Integrator Timer And Valve Control INVENTORS John N. StreetWIHmm I. Brody Walter clntosh ATTORNEY IMAGE MONITORING AND CONTROLSYSTEM CROSS-REFERENCE TO RELATED APPLICATION The present applicationcomprises a continuation in part of John N. Street application Ser. No.734,297 filed Jun. 4, 1968, for Image Monitoring and Control System.

BACKGROUND OF THE lNVENTlON Various forms of automatic processorsadapted to develop, fix, wash and dry sheets of photosensitive materialare already known to those skilled in the art. In such processors, asheet of photosensitive material to be processed is fed in sequence fromone processor tank to the next; and the developed, fixed and washedmaterial is then automatically passed'through a drier and collected. Inthe normal operation of such processors, the chemicals employed forprocessing the photosensitive material tend to become depleted as sheetsof such material are processed; and unless some form of chemicalreplenishment is effected during continued operation of the processor,there will be a severe degradation in the image quality of the filmsbeing developed.

It has been customary in the past to include some fonn of controllablereplenishment facility in automatic film processors, intended tomaintain chemical concentrations in the processor tanks at desiredvalues, or within desired limits. A variety of techniques andapparatuses attempted in the past for this general purpose have beendiscussed in the aforementioned prior copending application Ser. No.734,297; and this discussion, as well as the overall disclosure of saidprior copending application, is incorporated herein by reference. Ingeneral, prior manual and so-called automatic replenishment systemsexhibited various disadvantages and inaccuracies which preventedattainment of proper replenishment and maintenance of proper chemicalbalance.

A highly improved and far more accurate film processor replenishmentsystem has been disclosed in prior copending application Ser. No.734,297. In the system of this earlier application, a film processor isprovided with a sensor apparatus adapted to monitor the image densitythroughout the complete area of a film sheet after it has beendeveloped, and integrator means are provided for generating anelectronic signal commensurate with the monitored image density in suchfilm sheets. (The term sheet encompasses both continuous and cut lengthsof material, and the term film encompasses any suitable type of materialrequiring processing.) The complete area image density variations of thefilm sheet (or a plurality of such sheets), thus monitored, provide ahighly accurate measure of the degradation of the developer and fixersolutions of the processor; and a signal generated as a result of themonitoring operation is employed to control proper replenishment of saidsolutions.

The system of application Ser. No. 734,297 employs an optical scannercomprising an array of optical fibers which are illuminated in sequenceby a light source, and which cause an elongated narrow beam of light toscan repetitively the complete width of a sheet of film transported pastthe scanner after the sheet has been developed and fixed. Light passingthrough the developed film is detected by a further array of opticalfibers located on the opposite side of the film; and the detected lightis then transmitted via said further array to a photocell,photomultiplier tube, or like means. The photocell is coupled to a firstor fast" integrator adapted to produce a signal commensurate with thedeveloped areas sensed on the film during a single scan of the filmsheet by the sensor, and the output of this first integrator is sampledafter each lateral scan of the film. The sampled output of the fastintegrator is transferred to a second or slow" integrator arranged tostore and aggregate information corresponding to a plurality of lateralscans of the film sheet. The output of the second integrator is in turnapplied to a level detector and, when the output of the secondintegrator reaches a preselected level, the accumulated information inthe second integrator is transferred to a mechanical for furtheraccumulation. When a predetermined level of information has beenaccumulated in the mechanical integrator, a timer and replenishmentsolenoid valve system are energized to transfer replenishment chemicalsfrom storage tanks to the processor tanks for a fixed interval of timeand at preselected flow rates.

The general system described above incorporates light commutator andreed switching assemblies which are basically simple in concept, butcomplex in execution. The light commutator or scanner is driven directlyfrom the transport system of the film processor so that the sensorachieves its optical scanning at a rate related to the speed oftransport of the sheet through the processor; and this operates toproduce a constant number of scans per linear inch regardless oftransport speed. In addition, however, this arrangement presents therequirement for a variable integration time in the fast integrator, andthe system of the prior application accordingly employs a fastintegrator which incorporates a plurality of capacitors which areindividually selected for use in the integrator for various majortransport speed increments to compensate for the variable velocity scan.

This use of plural integrating capacitors represents a complexity in thesystem and, also, a source of possible inaccuracy since any onecapacitor can, at best, merely approximate the desired integration timeexcept at one particular speed. As will appear, this possible source oferror has been eliminated in the present invention through use of a newoptical scanner which operates at a constant scanning velocity; and thefast integrator is controlled to take fixed time-interval samples of thefilm density information, with the commencement of each samplingtime-interval being determined by the distance which a sheet of film hasbeen transported past the sensor, rather than by its speed of transport.These considerations permit the cmployment of a single integratingcapacitor in the fast integrator, and cause it to exhibit a fixedintegration time, regardless of possible variations in transport speedthereby reducing the complexity of the system and avoiding a possiblesource of er- IOl'.

The system of prior application Ser. No, 734, 297 also employs aplurality of fiber optics bundles distributed over a arc in the lightscanner; and these plural fiber optics bundles are scanned by a lightsource and associated rotary shutter having three equally-spacedidentical apertures. This arrangement necessitates relatively high costprecision machining procedures, and requires that extreme care be takenin fabrication of the scanner. An improved scanner is employed in thepresent invention which obviates these cost and assembly difficultiestTo assure accuracy, the system of the prior application contemplates theuse of regulated power supplies for energizing the lamp of the scanner,as well as for energizing the photomultiplier tube of the readingsensor. The need, and attendant cost, of such regulated supplies areeliminated in the present invention by the use of a novel zeroingarrangement operative to transmit a quantity of reference light to thephotomultiplier tube at the end of each active scan, and associated witha control circuit incorporating a dynode voltage feedback loop operativeto maintain the photomultiplier tube anode current, and therefore itslight sensitivity, at a constant value.

The system of the earlier application, moreover, contemplates the use ofthree rotating magnets to obtain identical actuation of two reedswitches for effecting various control functions during the monitoringand information accumulation steps. These mechanical considerations havebeen found to present major problems during production, involving theaccurate balancing of magnets, plural reed switches, etc. in the presentinvention, an improved electronic circuit is employed which eliminatesthe use of one reed switch and all rotating magnets. To achieve a morereliable and predictable operation of the remaining switch, a differentmeans of switch actuation has been adopted, involving the use of astationary magnet which has its field interrupted by a shunt-typerotating aperture plate.

SUMMARY OF THE INVENTION The system of the present invention isgenerally similar to the arrangement discussed above and disclosed inprior copending application Ser. No. 734,297. While the generalorganization and theory of operation of the system is the same as thatdescribed in said earlier application, a number of significant changeshave been made.

In the system of the present invention scanning of the developed filmoccurs at a constant speed to provide a constant scan time. The linescanning rate is maintained at a fixed value, irrespective of the filmtransport speed, by means of a constant-velocity mechanical scannerdriven by a motor having its speed of rotation synchronized by a powersource of stable frequency, e.g., the power-line frequency.

The fast integrator ofthe present invention is revised to employ only asingle capacitor of fixed value, whereby the fast integrator exhibits apredetermined and constant integration characteristic. The fastintegrator is turned on" for a time period equal to one scan line(approximately 100 milliseconds for a scanner rotational speed of 600rpm. once every 0.1 inch of linear film travel through the sensingstation. This control of the fast integrator is achieved by means of aone-shot multivibrator and an associated reading gate which aretriggered by a transport pulse generator operated by the processortransport system. The fast integrator is thus caused to accumulateinformation corresponding to a single scan, as in the earlier system,but it does so without the complexity of plural reed switches androtating magnets,-and without the inaccuracies which are certain toarise through use of a variable integration time.

The improved system of the present invention incorporates, moreover, arebalancing (or zeroing) circuit which employs an extra fiber opticsbundle extending between the scanning light source and thephotomultiplier tube, but located outside of the film path, for exposingthe photomultiplier tube to a reference light level during a portion ofeach scan. The difference between the output current of thephotomultiplier tube and that ofa stable reference current source iscoupled, during the zeroing time interval, to a sampling amplifier whichcontrols a feedback circuit operative to adjust the photomultiplier tubedynode potential immediately prior to the commencement of each activeline scan. As a result, the system operates to maintain a constant valueof photomultiplier tube anode current and a predetermined opticalsensitivity, irrespective of line voltage variations and/or lampbrightness changes. This permits the system to dispense with costly andcomplex regulated power supplies without affecting the accuracy oftheoverall monitoring and integration operunons.

A number of additional improvements are made to reduce the cost of theoverall system, to reduce maintenance requirements, and to make thesystem more easy to manufacture, set up, and operate. As discussedearlier, one of the reed switches and all of the rotating magnetsemployed in the arrangement ofthe earlier application have beeneliminated, and a different means of actuation is employed for theremaining switch, comprising a stationary magnet associated with ashunt'type rotating magnetic-aperture plate. The separate level detectorof the earlier circuit has been simplified, and is partially combinedwith the slow integrator. In addition, the sensor is now constructed toexhibit a new distribution of fiber optic bundles, relative to the lightsource, to simplify fabrication of the scanner; and the sensor bundlesthemselves are constructed in a modular form at the transmitter andreceiver sensor portions of the system to facilitate sensor installationand replacement of faulty optical bundles.

By the various changes discussed above, the overall system has beensimplified and reduced in cost, and, at the same time, its stability andreliability have been improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an illustrative view of animproved scanner and zeroing arrangement constructed in accordance withthe present invention;

FIG. 2 is another view of the scanner and zeroing arrangement of FIG.1', and

FIG. 3 is a circuit diagram of an improved control system constructed inaccordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODItVl ENTS As is discussed in priorcopending application Ser. No. 734,297, identified earlier, thedescription of which is incorporated herein by reference forcompleteness, an automatic film processor employing the improvedautomatic replenishment control ofthe present invention may comprise aplurality of processor tanlts including at least one developing tank, atleast one fixing tank, and at least one wash tank. Exposed sensitizedmaterial to be developed is fed in sequence through the several tanks bymeans of an appropriate transport system; and the transport drive shaftfor such a system has been designated 10 in FIG. 1. Squeegee rollerpairs 11 and 12 may be located downstream of the wash tank in theprocessor; and the developed film 13 is caused to pass through saidsqueegee roller pairs by means ofa worm drive 14 carried by shaft 10, toachieve surface moisture removal from film 13 before it is finally driedand collected.

As is discussed in prior copending application Ser. No. 734,297, sensorarrangement is provided adjacent the squeegees to inspect or monitoreach sheet of film 13 throughout both its width and length thereby todetermine the optical image densities developed in the film by theprocessor action. This provides information constituting a measure ofthe amount of chemical which has been used in the course of thedevelopment process, and this information is accumulated during themonitoring operation and used to control chemical replenishment in theprocessor. An improved sensor is used in the present invention; and apreferred embodiment is shown in FIGS. 1 and 2.

The sensor of the present invention employs an improved scannercomprising a stationary light-tight lamp housing 15 provided, on itsinterior, with a concentric drumlike shutter member 16. A lamp 17 issupported within drum l6; and lamp 17 may comprise, for example, a 50watt lamp energized by a 12 volt DC source 18. Lamp 17 may emit whitelight, or may have other spectral characteristics eg red light), or maybe associated with any appropriate light filter. As will appearsubsequently, source 18 need not be a regulated source. A blower 15a isattached to housing 15 for cooling purposes.

In the scanner employed in prior application Ser. No. 734,297, ten lightcommutating stations were distributed over a arc, and were scanned bythree equallyspaced idcnti cal apertures provided in a drum analogous todrum 16. This arrangement necessitated high-cost precision machiningprocedures. In the improved arrangement of FIG. I, drum in is providedwith only a single aperture 19, and light from lamp 17 passing throughaperture 19 is caused to impinge upon sue cessive ones of a plurality of13 light-commutating stations which are equally spaced through 360 abouthousing I5. More particularly, the 13 light-commutating stationscomprise 12 light-transmitting fiber optics bundles 20 which constituteportions of the transmitting sensor, and a thirteenth bundle 21constituting a zeroing bundle the function of which will become apparentsubsequently.

The 13 bundles 20 and 21 each have one end thereof plugged into housing15 in a circular array (see FIG. 2) and in a plane passing throughshutter aperture 19. Drum 16 is mounted for rotation within housing 15,and is driven by a shaft 22 connected, for example, to a 600 rpm.synchronous motor 23 which is energized and synchronized, for example,by a 60 Hz source 24. By this arrangement, drum 16 is caused to rotateat a constant speed; and light passing from lamp l7 through aperture 19is caused to impinge in succession and at a constant repetition rate onthe ends of bundles 20 and 21 which are plugged into housing 15.

The 12 bundles 20 have their other ends connected, in groups of three tofour transmitter sensor modules 25, 26, 27

and 28 disposed in side by side relation to one another on one side ofthe path of travel of film 13. The several modules 25 through 28 areindividually replaceable; and each such module may be 6 inches in lengthso that the four modules cooperate with one another to transmit lightthrough film 13 over a total width of 24 inches. The fibers in eachindividual bundle are, within the body of each module, fanned out toform a line; and as light from lamp 17 impinges on each of the bundles20 in succession, a narrow rectangle of light is directed onto the sheetof film 13, and scans across said sheet at a constant speed determinedby the speed of rotation of drum 16.

The system also includes a reading sensor comprising 12 fiber opticsbundles 30 constructed to form four reading sensor modules 31-34disposed in aligned relation to one another below film 13 and below thetransmitter sensor modules -28. The several modules 31-34 are, again,individually replaceable, and each such module comprises a group ofthree fiber optics light receiving bundles the fibers of which arefanned out linearly.

The ends of bundles 30, remote from film 13, are individually pluggedinto a light-tight housing containing a photomultiplier tube 36, or anyother appropriate light sensing element. The light which passes throughfilm 13 from each segment of transmitter sensor modules 25-28 iscollected by a corresponding segment in receiver modules 31-34 and thenpassed via fiber optics bundles 30 to photomultiplier tube 36. By thisgeneral arrangement, and as described in greater detail in priorapplication Ser. No. 734,297, a measure of the image density in film 13,encountered during each individual scan of the film, can be obtained.

The zeroing bundle 21, one end of which is plugged into housing 15 ofthe scanning light source, has its other end plugged into housing 35 ofphotomultiplier tube 36 in a manner similar to that employed forplugging the analogous such ends of bundles 30 into housing 35. Moreparticularly, each bundle 21 and 30 plugs into the photomultiplier tubehousing 35 by means of a fitting provided with an adjustment screwdiagrammatically illustrated at 37. 'Each such adjustment screw has afree end which is variably positionable relative to the emitting end ofits associated bundle; and by rotation of each screw 37, it is possibleto selectively attenuate the light received by photomultiplier tube 36from a given bundle. The several screws 37 are initially adjustedso thatthe light emitted from all of bundles 30, and from zeroing bundle 21,will have the same identical value in the absence of film sheet 13, andthis initial adjustment of the light received by tube 36 from theseveral bundles 21 and 30 assures that zeroing bundle 21 will alwaysprovide an appropriate magnitude of reference light from the scanninglight source 15-19, for zeroing the overall system.

The output of the photomultiplier tube arrangement 35, 36 is coupled toa control circuit 40, which will be described in greater detailsubsequently in reference to FIG. 3. Circuit 40 includes a switch 41which may comprise a reed switch; and switch 41 is actuatedmagnetically. In accordance with the improvement of the presentinvention, drive shaft 22 of the scanning light source carries a disc 42fabricated of a magnetic material. A permanent magnet 43 is located onone side of disc 42, and switch 41 is located on the other side of saiddisc 42. Disc 42 is provided with an aperture 44. When aperture 44 is,during rotation of disc 42, disposed between switch 41 and stationarymagnet 43, the field of magnet 43 can actuate switch 41. For otherpositions of disc 42, however, the magnetic material of said disc actsas a magnetic shunt to prevent the field of magnet 43 from actuatingswitch 41. By this arrangement, therefore, switch 41 is actuated onceduring each revolution of drum 16. As will appear hereinafter, the timeat which switch 41 is actuated corresponds very precisely to the timeduring which light is being projected onto zeroing bundle 21.

In accordance with the improvement of the present invention, film sheet13 is scanned at a fixed rate as already described; and the system ofthe present invention is caused to take fixed time-interval samplesperiodically, with the commencement time for each sample beingdetermined by the distance a sheet has been transported through theprocessor (or past sensor 25-28, 31-34) rather than being determined bythe speed of transport. In order to monitor the distance each sheet hasbeen transported past the sensor, a transport pulse generator 45 isprovided. Generator 45 is actuated from transport drive shaft 10 of thesystem and operates to produce a triggering pulse 46 once every 0.] inchof linear film travel through the sensing station, Transport pulsegenerator 45 can, of course, take various forms. In onepossiblearrangement, generator 45 may comprise a stationary reed switch, astationary magnet, and a rotary magnetic shunt disposed between the twoand driven by the transport system so that the reed switch is actuatedeve'ry one-tenth of an inch of film travel by an operation entirelysimilar to that of elements 41-44 already described. Pulse 46, when itoccurs, is coupled to control circuit 40 and, as will be described, isused to trigger a one-shot multivibrator which in turn controls areading gate associated with the fast integrator of the system.

FIG. 3 illustrates control circuit 40 in some detail, and shows therelationship of that control circuit to photomultiplier tube 36. Thegeneral operation of the FIG. 3 circuit corresponds to that alreadydescribed in prior copending application Ser. No. 734,297 and willtherefore not be repeated in detail. Structurally, the arrangementincludes photomultiplier tube 36 which is exposed to light fromreceiving sensor bundles 30 and zeroing bundle 21 in sequence; and theoutput from photomultiplier tube 36 is selectively coupled to a fastintegrator comprising an operational amplifier 50 connected as shown toa capacitor 51. The output of fast integrator 50- 51 is coupled to aslow integrator comprising operational amplifier 52 and a capacitor 53;and the output of slow in tegrator 52-53 is coupled to a level detector54, comprising a Zener diode 54a and transistor 54b plus associatedcomponents, which ultimately controls energization of a transistor 55operating as a driver for a relay 56. Relay 56, when energized, operatesinter alia to transfer information from the slow integrator 52-53 via aline 57 to the input ofa mechanical in tegrator 58; and mechanicalintegrator 58in turn controls the operation of a timer and valve controlmechanism 59 which achieves replenishment in the automatic filmprocessor.

Since the main scanner lamp 17 is energized by an unregulated powersupply, the lamp output will vary with variations in line voltage. Theseoutput light variations, and other similar variations resulting from theaccumulation of foreign matter on the lamp surfaces, manifest themselvesas variations in the light output at each of the 12 transmitter sensorbundles 20, as well as a similar light output variation at thethirteenth zeroing bundle 21. Photomultiplier tube 36 is energized by anunregulated source 60 (e.g. lkv); and variations in energization of tube36 have a major effect on the output of said tube 36. These effectscould be minimized, of course, through use of regulated power supply;but it is preferred, if possible, to use unregulated supplied tosimplify the overall system, and reduce its cost. The use of suchunregulated power supplies becomes feasible by means of the zeroingsystem which is incorporated into the present invention.

The zeroing operation employs, as described, an extra bun dle of fiberoptics 21 which extends from the scanning light source 15-19 to thephotomultiplier tube 36. Zeroing bundle 21 can be entirely separate fromthe film sensor structure or, in the alternative, can comprise a portionof the film sensor structure wherein the optical path of the zeroingbundle is located outside of the film path. The Zeroing system isintended to compensate the entire system against possible errorsresulting from line voltage variations, and from any other effects whichmay be present and which may tend to change the output of thephotomultiplier tube 36, In essence, the zeroing zeroing adjustment ismaintained intermediate successive receptions of light from the zeroingstation 21 due to the relatively long time constant of the overallsystem achieved by a capacitor 60.

in general, the zeroing system incorporates a sample and store capacitor60, a zeroing amplifier 61, and a dynode shunt regulator employing adriver transistor 62. Amplifier 61 selectively modifies thephotomultiplier tube dynode potential via the shunt voltage regulatorarranged in a negative feedback loop so as to electronically rebalancethe lamp-photomultiplier tube sensing system immediately prior to thecommencement of each active scanning line, thereby to maintain aconstant value of photomultiplier tube anode current and opticalsensitivity irrespective of line voltage variations and/or lampbrightness changes. When the overall system is first placed intooperation, the desired anode output reference current of tube 36 isinitially established by adjusting a variable resistor 63 extendingbetween source 64 and the anode 65 of tube 36. Resistor 63 comprises acompensation current balance con trol, and can be set so that theeffective output supplied to the blade of switch 41 is zero, or anyother predetermined reference value; and the zeroing system thenoperates to assure that this preselected value of current is produced atanode 65 and switch 41 in response to exposure of tube 36 to apredetermined quantity of light.

The zeroing operation occurs as follows: when the light scanner applieslight from lamp 17 onto the zeroing bundle 21, light transmitted viabundle 21 is directed onto the cathode 66 of tube 36. During this sameinterval of time, when light is being received from the zeroing bundle21, the reed switch 41 is magnetically actuated so that its blade is inthe lower position, and compensated anode current is accordingly coupledfrom tube 36 to capacitor 60 to charge that capacitor. The movable bladeof switch 41 transfers to its upper position immediately after thezeroing bundle has been scanned, and this operates to transfer theoutput of the photomultiplier tube 36 to the fast integrator 50-51 fornormal operation during the remainder of the scan operation.

If the actual current applied to the blade of switch 41 during thezeroing operation corresponds to the preadjusted output achieved earlierby means of compensation current balance control 63, there will be noeffective change in the charge maintained in sample-and-store capacitor60, and zeroing amplifier 61 will have no effect on the dynode voltageof tube 36. Let us assume, however, that something has occurred whichhas caused the output of the photomultiplier tube 36 to increase. Duringthe zeroing operation, the increased output of tube 36 causes anincrease in the charge maintained in capacitor 60; and this in turnincreases the output of zeroing amplifier 61 to increase the output ofdriver transistor 62 in the dynode shunt regulator. The increasedconduction of transistor 62 reduces the effective dynode voltage of tube36, and thereby reduces the output reference-level current of thephotomultiplier tube to its desired value. Conversely, if the lightoutput from the photomultiplier tube should decrease, the dynode voltageis effectively increased to similarly restore the reference-level anodecurrent to its desired value.

By this type of feedback regulation, the dynode voltage of tube 36 isadjusted during each zeroing interval of the system to assure that theanode current of the photomultiplier tube is at a desired referencevalue during the subsequent scan, and the output then varies from thatreference value in accordance with the detected density of film 13during said subsequent scan. Inasmuch as the system is rebalanced at thebeginning of each active scan, there is no need for elaborate andexpensive regulated power supplies.

After zeroing operation, the blade of reed switch 41 trancfers to theposition shown in FIG. 3 to couple the adjusted output ofphotomultiplier tube 36 to the input of the fast integrator 50-51. lnthe improved arrangement of the present invention, integrator 50-51 hasa fixed integration time determined by the single capacitor 51, therebyavoiding the approximations and possible errors which attended the useofa variable integration time in the arrangement of prior applicationSer. No. 73,297.

Operational amplifier 50 is shunted by a normally-conducting transistor70 which prevents the fast integrator from accumulating any chargeacross capacitor 51. Transistor 70 comprises a reading gate, and isselectively cut off for a fixed time period at intervals correspondingto each 0.1 inch of film travel past the sensor. More particularly, eachpulse -36 produced by the transport pulse generator 45 triggers aoneshot multivibrator 71 having a period of milliseconds. Whenmonostable multivibrator 71 produces an output at 72 during its on"time, normally-conductive transistor 73 is rendered nonconductive; andthis in turn cuts off reading gate transistor 70 and permits theaccumulation of a charge across fast integrator capacitor 51 during thenext succeeding 100 milliseconds. The lOO milliseconds during which fastintegrator capacitor 51 accumulates a charge actually corresponds to thetime needed to complete one active scanning line; and therefore fastintegrator 50-51 accumulates information corresponding to a singlescan,just as in the earlier system of Ser. No. 734,297, but without thecomplexity of plural reed switches, etc.

lt should be noted that because of the constant velocity of the lightscan, and the possible variations in speed of film transport, the actualsampling period for any one line of information does not necessarilycommence at the beginning of that line but can, indeed, commence atalmost any part of the line and at different parts of the line as thetransport speed varies. Nevertheless the total information accumulatedbetween the beginning and end of each sample always corresponds to asingle line of information regardless of the precise point on that lineat which the sample commences. Thus the present invention, by scanningat a constant velocity, and by using an integrator having a fixedintegration characteristic, assures that information is accumulated moreaccurately despite possible variations in film transport speed past thesensor.

Slow integrator 52-53 of the present invention is also revised somewhatfrom that described in earlier application Ser. No. 734,297, but theoperation is still effectively the same. In the earlier circuit, aseparate operational amplifier was used as a level detector. Thearrangement shown in FIG. 3 utilizes a revised transistor circuit whichpartially combines the separate level detector with the slow integratorto form a regenerative trigger circuit which performs the same functionas the earlier circuit. When the output of the slow integrator stage52-53 reaches a potential level determined by the level detector Zenerdiode 54a, transistor 54b, which is normally nonconductive, is renderedconductive; and transistor 55, which is normally nonconductive, issimilarly rendered conductive to energize the coil of relay 56. At thesame time that transistor 54!; is rendered conductive, i.e., at the timethat the desired potential level has been reached at the output of slowintegrator 52, a signal is fed back via line 54c to the inverting inputof integrator 52 to drive the integrator to its maximum output value. Itwould remain at this value except for the fact that, when relay 56 isenergized, relay contacts 560 are closed to short circuit capacitor 53and to restore the slow integrator to its starting condition. At thesame time, upon energization of relay 56, relay contacts 56b generate apulse which is fed to the input of the mechanical integrator 58 whichaccumulates information in the manner already described in earlierapplication Ser. No. 734,297.

The general operation of mechanical integrator 58, and of timer andvalve control mechanism 59, and one possible circuit which can be usedfor these components, is set forth in prior application Ser. No.734,297, which is incorporated herein by reference.

While we have thus described a preferred embodiment of the presentinvention, many variations will be suggested to those skilled in theart. lt must therefore be emphasized that the foregoing description isintended to be illustrative only and not limitative of the presentinvention; and all such variations and modifications as are in accordwith the principles described are meant to fall within the scope of theappended claims.

We claim:

1. A chemical replenishment system for a film processor, comprisingsensor means adjacent said processor for monitoring the image density insheets of image-bearing material developed in said processor, means fortransporting each such developed developed sheet past said sensor means,said sensor means including means for optically scanning each sheetrepetitively and at a fixed speed, accumulating means coupled to saidsensor means for accumulating information related to the image densityof each such sheet and to the aggregate densities of a plurality of suchsheets, said accumulating means including means for periodicallysampling the output of said'sensor means as a function of the distanceeach such sheet is transported past said sensor means, and control meansresponsive to said accumulated information for selectively controllingthe feeding of replenishment chemical to said processor.

2. The system of claim 1 wherein said sensor includes a photomultipliertube, and means for automatically adjusting the output of said tubeduring each of said repetitive scans.

3. The system of claim 1 wherein said accumulating means includes anormally inoperative electronic integrator circuit,

, said sampling means including triggering means for rendering saidcircuit operative to store information.

4. The system of claim 3 wherein said integrator circuit includescapacitor means, a normally conductive transistor shunting saidcapacitor means for rendering said integrator circuit inoperative, saidtriggering means including pulse generator means controlled by saidtransporting means for producing a triggering pulse upon occurrence of apreselected increment of travel of said sheet past said sensor means,and means responsive to occurrence of each such triggering pulse forrendering said transistor non-conductive for a predetermined timeinterval.

5. The system of claim 4 wherein said last-named means comprises amonostable multivibrator.

6. The system of claim 1 wherein said sensor means comprises a lightsource, a first plurality of bundles of optical fibers having one end ofeach such first bundle disposed adjacent said light source, scanningmeans for directing said light source in sequence and at a constantspeed onto said one ends of said first bundles, the other ends of saidfirst bundles being disposed adjacent one side of the path of travel ofeach such sheet past said sensor, a second plurality of bundles ofoptical fibers having one end of each such second bundle disposedadjacent the other side of said path of travel of said sheet, the otherends of said second plurality of bundles being disposed adjacent aphotosensitive element, and means coupling the output of saidphotosensitive element to the input of said accumulating means.

7. The system of claim 6 including a further bundle of optical fiberspositioned outside the path of travel of said sheet and extendingbetween said light source and said photosensitive element forperiodically exposing said photosensitive element to reference lightfrom said light source, and control means operative during the timeinterval of said reference light exposure for adjusting the outputcurrent of said photosensitive element to a preselected value.

8. The system of claim 7 wherein said photosensitive element comprises aphotomultiplier tube, said control means ineluding means for varying thedynode voltage of said photomultiplier tube.

9. The system of claim 7 wherein said one ends of said first bundles andone end of said further bundle are regularly spaced from one another ina circular array about said light source, said scanning means comprisinga rotary motordriven, apertured shutter disposed between said array andsaid light source.

1. A chemical replenishment system for a film processor, comprisingsensor means adjacent said processor for monitoring the image density insheets of image-bearing material developed in said processor, means fortransporting each such developed developed sheet past said sensor means,said sensor means including means for optically scanning each sheetrepetitively and at a fixed speed, accumulating means coupled to saidsensor means for accumulating information related to the image densityof each such sheet and to the aggregate densities of a plurality of suchsheets, said accumulating means including means for periodicallysampling the output of said sensor means as a function of the distanceeach such sheet is transported past said sensor means, and control meansresponsive to said accumulated information for selectively controllingthe feeding of replenishment chemical to said processor.
 2. The systemof claim 1 wherein said sensor includes a photomultiplier tube, andmeans for automatically adjusting the output of said tube during each ofsaid repetitive scans.
 3. The system of claim 1 wherein saidaccumulating means includes a normally inoperative electronic integratorcircuit, said sampling means including triggering means for renderingsaid circuit operative to store information.
 4. The system of claim 3wherein said integrator circuit includes capacitor means, a normallyconductive transistor shunting said capacitor means for rendering saidintegrator circuit inoperative, said triggering means including pulsegenerator means controlled by said transporting means for producing atriggering pulse upon occurrence of a preselected increment of travel ofsaid sheet past said sensor means, and means responsive to occurrence ofeach such triggering pulse for rendering said transistor non-conductivefor a predetermined time interval.
 5. The system of claim 4 wherein saidlast-named means comprises a monostable multivibrator.
 6. The system ofclaim 1 wherein said sensor means comprises a light source, a firstplurality of bundles of optical fibers having one end of each such firstbundle disposed adjacent said light source, scanning means for directingsaid light source in sequence and at a constant speed onto said one endsof said first bundles, the other ends of said first bundles beingdisposed adjacent one side of the path of travel of each such sheet pastsaid sensor, a second plurality of bundles of optical fibers having oneend of each such second bundle disposed adjacent the other side of saidpath of travel of said sheet, the other ends of said second plurality ofbundles being disposed adjacent a photosensitive element, and meanscoupling the output of said photosensitive element to the input of saidaccumulating means.
 7. The system of claim 6 including a further bundleof optical fibers positioned outside the path of travel of said sheetand extending between said light source and said photosensitive elementfor periodically exposing said photosensitive element to reference lightfrom said light source, and control means operative during the timeinterval of said reference light exposure for adjusting the outputcurrent of said photosensitive element to a preselected value.
 8. Thesystem of claim 7 wherein said photosensitive element comprises aphotomultiplier tube, said control means including means for varying thedynode voltage of said photomultiplier tube.
 9. The system of claim 7wherein said one ends of said first bundles and one end of said furtherbundle are regularly spaced from one another in a circular array aboutsaid light source, said scanning means comprising a rotary motor-driven,apertured shutter disposed between said array and said light source.